This invention relates to an improved towplate system for controlling the initiation of low altitude parachute extraction of cargo from an aircraft.
The patents to Cotton, U.S. Pat. No. 3,113,571; Kriesel, U.S. Pat. No. 3,396,924; Leger, U.S. Pat. No. 3,670,999; Hosterman et al., U.S. Pat. No. 3,801,051; and Fielding et al., U.S. Pat. No. 3,865,333, disclose various systems used in the extraction of cargo from an aircraft.
In the extraction of aircraft cargo at low altitudes a drogue parachute is first towed and then released, which acts to deploy the main parachute extraction system. One mechanism for coupling the drogue parachute to the main parachute, which was built for the Department of the Air Force, is called the Oxford towplate. It employed a two part force transfer link assembly having a first link member connected to the drogue parachute line and a second link member connected to a transfer line which, in turn, was connected to the main parachute. The two link members were also detachably coupled together. The Oxford towplate further employed a link release mechanism attached to the aircraft floor for retaining the link assembly until actuated for release of the assembly and thus the main parachute.
The link release mechanism was actuatable either electrically (automatically) or manually for causing release of the two-part link assembly. For electrically actuating the link release mechanism, a solenoid was coupled to a pivotal retainer member or latch of the release mechanism. When the solenoid was deenergized it positioned the retainer member in engagement with the two part link assembly so as to lock it into the link release mechanism. Upon being energized, the solenoid would pivot the retainer member away from the link assembly, allowing the deployed drogue parachute to then extract the link assembly from the release mechanism. The solenoid was selectively energized and deenergized by a switch located in the cockpit for use by the pilot.
Should the electrical circuit for the solenoid, or the solenoid itself, malfunction, a manual force transfer lever was provided, being connected by a push-pull cable to linkage in the link release mechanism. By moving the lever so as to pull the cable, the retainer member was manually pivoted away from the two part link assembly. The link assembly was then unlocked and extractible from the release mechanism by the drogue parachute. If some malfunction occurred or if conditions changed such that it was undesirable to deliver the cargo, a drogue release lever was provided to jettison the drogue parachute. The drogue release lever was connected by another push-pull cable to other linkage in the release mechanism for actuating cooperable pins which detachably coupled the first and second link members of the force transfer link assembly together. By moving the drogue release lever to pull its cable the second link member was manually detached from the first link member allowing the drogue parachute to be jettisoned without unlocking the first link from the release mechanism.
Effective performance of either of the above-described manual operations through use of the appropriate one of the two separate levers of the Oxford towplate required that the other lever be fully returned to a neutral position before the one lever was moved. Otherwise the linkage of the link release mechanism connected to other lever might interfere with or obstruct the performance of the one lever whether it be to transfer force from the drogue to the main parachute or release the drogue parachute alone. In field trials of the Oxford towplate, it was found that frequent adjustments needed to be made to the cables and linkages connected to the levers and even then satisfactory operation of the towplate could not be ensured.